arXiv subjects

Oleg A. Tretiakov

Publications and source records attributed to Oleg A. Tretiakov.

At least 19 recordsLinked to original sources

arXiv2026

Inertial Dynamics of a Skymeron

Topological spin textures in antiferromagnets inherit the compensated magnetic order of the host material, resulting for skyrmions in the suppression of the skyrmion Hall effect and enabling ultrafast dynamics that make them attractive for low-power spintronic devices. In intrinsic antiferromagnets, the two sublattices are identical, but synthetic antiferromagnets offer additional control mechanisms by enabling independent tuning of the properties of two ferromagnetic layers. Analogous to a ferrimagnet, the total magnetic moment can be adjusted by compensating the two-layer moments. Here, we demonstrate that tuning the effective magnetic anisotropy difference between the two layers drives a spin-flop transition where one layer reorients and thus stabilizes an orthogonal configuration with one layer oriented along the out-of-plane direction and the other in-plane. In this transition, an antiferromagnetic skyrmion undergoes a homotopic reconfiguration into a complex spin texture comprising a skyrmion coupled to an in-plane bimeron. Element-specific X-ray microscopy resolves this texture layer by layer: one hosts an out-of-plane skyrmion coupled to an in-plane bimeron in the other. We refer to this previously unexplored three-dimensional spin texture as a skymeron. By using time-resolved pump-probe X-ray microscopy, we discover unique polarity ,dependent dynamics during current pulses: a short post-pulse inertia-like continuation of the motion, and a slower return towards the pinned initial state. Micromagnetic simulations reveal that the inertia-like propagation originates from the finite-time relaxation of reorientation of the skymeron. Our results establish layer-selective anisotropy engineering as a route to uncharted composite spin textures with internal dynamical degrees of freedom, not possible in conventional antiferromagnets with identical sublattices.

cond-mat.mes-hall↗

arXiv2026

Unveiling Three-Dimensional Skyrmion Transitions Through Vortices and Monopoles

Magnetic skyrmions represent vortex-like spin configurations that provide a robust platform for next-generation spintronic technologies. Although they are often treated as two-dimensional objects with integer topological charge, their extension into three-dimensional strings realizes other composite structures with unique device functionalities that transcend planar frameworks. Unfortunately, a lack of bulk probes has failed to realize such higher-dimensional topological structures and their implementations. Here, we report the first experimental visualization of three-dimensional topological $Q = 0$ skyrmion structures using neutron scattering tomography techniques across the equilibrium phase of a Co$_8$Zn$_8$Mn$_4$ sample. Disordered skyrmion states reveal metastable skyrmioniums and composite topological objects novel to bulk systems. Vortex-antivortex lattices mediate changes in topology, with unprecedented transition pathways via a coupling of merons and monopoles. The present realization of bulk Q = 0 quasiparticles and meron-mediated dynamics paves the way for higher-dimensional spintronic frameworks through multi-bit encoding architectures, unidirectional transport schemes, and monopole-mediated controls.

cond-mat.mes-hall↗

arXiv2026

Helicity-Controlled Hall Transport in Hybrid Topological Magnetic Textures

Topological magnetic textures can serve as information carriers driven by spin currents. However, their motion is generally accompanied by a Hall effect that deflects them from the current direction, limiting transport efficiency and controllability. We develop a unified spin-space transformation framework enabling a systematic study of hybrid spin textures with different helicities, such as skyrmions, antiskyrmions, bimerons, and antibimerons. Combining analytical theory with micromagnetic simulations, we establish the relation between helicity and current-driven transport. An analytical solution of the generalized Thiele equation identifies helicity as a geometric control parameter and yields a simple expression for the Hall angle, enabling its continuous tuning, complete suppression, and deterministic steering along arbitrary in-plane directions. Micromagnetic simulations confirm that the generated spin textures remain stable under Landau--Lifshitz--Gilbert dynamics and validate the analytical predictions. These results establish helicity as a versatile control parameter for programmable transport of topological magnetic textures.

cond-mat.mes-hall↗

arXiv2026

Quantum encoding of structured light into in-plane topological spin textures

Structured light offers a powerful means of controlling light-matter interactions through multiple tunable optical degrees of freedom. Using micromagnetic simulations, we investigate the nucleation of asymmetric bimerons and antibimerons by pulsed Laguerre-Gaussian optical vortices in chiral ferromagnetic thin films with $C_{nv}$ and $D_{2d}$ symmetries, respectively. For optical vortices with orbital angular momentum (OAM) $|m|=1$, circularly polarized beams deterministically nucleate a single bimeron or antibimeron via the interplay of spin angular momentum, OAM, and magnetic chirality, whereas linearly polarized beams produce textures whose topological charge directly follows the OAM ($Q=m$). Optical vortices with OAM $|m|>1$ nucleate clusters and other configurations composed of multiple spin textures, whose morphology and topological charge depend sensitively on the optical quantum numbers and pulse parameters. These findings reveal a route to topology-selective writing through the encoding of optical quantum numbers into distinct in-plane topological magnetic states.

cond-mat.mes-hall↗

arXiv2026

Asymmetric Antibimerons: Statics and Dynamics

Nontrivial topological spin textures, such as magnetic skyrmions, are of great interest due to their potential use as information carriers in spintronic memory and logic. Here, we theoretically predict an asymmetric antibimeron (AAB) -- a topological texture in an in-plane magnetized chiral ferromagnet with $D_{2d}$ symmetry, which has yet to be observed experimentally. We show that AABs can be stabilized by an anisotropic interfacial Dzyaloshinskii-Moriya interaction, characteristic of materials with $D_{2d}$ symmetry. Using energy considerations, we explain the origin of its asymmetric shape, composed of an antivortex and a crescent-shaped vortex with opposite core polarizations. Furthermore, we demonstrate that AABs of opposite topological charge can coexist within the same ferromagnetic film, in contrast to skyrmions in out-of-plane magnetized systems. Employing micromagnetic simulations and an analytical approach based on an extension of Thiele's equation to a system of two elliptic merons comprising the AAB, we are able to describe the current-driven dynamics of AABs. In particular, we show that AAB collisions enable controlled manipulation of the system's topological charge. Our findings shed light on fundamental understanding of asymmetric topological magnetic solitons and provide a roadmap for their experimental observation in in-plane magnetized ferromagnets.

cond-mat.mes-hall↗

arXiv2026

Topology-constrained spin-wave modes of asymmetric antibimerons and their clusters

Collective modes are a defining signature of coupled degrees of freedom, forming a bridge between understanding of interactions in condensed-matter systems and emergent functionality. Topological magnetic textures provide a natural platform to realize and control such collective modes at the nanoscale. Here we theoretically identify and characterize low-energy collective spin-wave excitations of isolated asymmetric antibimerons and their clusters in ultrathin ferromagnetic films. We demonstrate that an isolated asymmetric antibimeron supports a discrete spectrum of localized modes, reflecting its internal degrees of freedom. When multiple asymmetric antibimerons form a cluster, inter-texture coupling leads to the splitting of these modes into $N$-fold multiplets, where $N$ denotes the number of asymmetric antibimerons. To rationalize these findings, we introduce an effective coupled-oscillator model based on meron pairs that captures the essential collective dynamics of the system. This emergent classical mechanics description reveals that the motion of asymmetric antibimeron clusters can be understood in terms of well-defined normal modes governed by topology-constrained particle-like degrees of freedom. These results establish coupled asymmetric antibimerons as a tunable platform for spin-wave based nano-oscillators, whose normal-mode spectrum is controllable through cluster size, thus providing a programmable set of low-lying resonances for these nano-oscillators.

cond-mat.mes-hall↗

arXiv2026

Emergent electric field induced by dissipative sliding dynamics of domain walls in a Weyl magnet

The dynamic motion of topological defects in magnets induces an emergent electric field, as exemplified by the continuous flow of skyrmion vortices. However, the electrodynamics underlying this emergent field remains poorly understood. In this context, magnetic domain walls - one dimensional topological defects with two collective modes, sliding and spin tilt - offer a promising platform for exploration. Here, we demonstrate that the dissipative motion of domain walls under oscillatory current excitation generates an emergent electric field. We image domain patterns and quantify domain wall length under applied magnetic fields in mesoscopic devices based on the magnetic Weyl semimetal NdAlSi. These devices exhibit exceptionally strong domain wall scattering and a pronounced emergent electric field, observed in the imaginary component of the complex impedance. Spin dynamics simulations reveal that domain wall sliding dominates over spin tilting, where the phase delay of the domain wall motion with respect to the driving force impacts the emergent electric field. Our findings establish domain-wall dynamics as a platform for studying emergent electromagnetic fields and motivate further investigations on the coupled motion of magnetic solitons and conduction electrons.

cond-mat.mes-hall↗

arXiv2025

Interplay of magnetic textures with spin-orbit coupled substrates

Magnetic textures such as skyrmions in thin films grown on substrates possess significant technological potential. Inhomogeneous magnetic structures can be described as homogeneous ferromagnetic order in the presence of anisotropic spin-orbit coupling (SOC). It remains unexplored, however, how this {\it induced} SOC stemming from the magnetic textures interacts with the SOC of the substrate. Here we show that these two contributions to SOC are in general {\it not} additive. We demonstrate this by employing a spintronics gauge theory. We further compute local currents which, when considered in the proper frame, match the spintronics gauge theory results. Finally, we analyze global transport quantities and show that they substantiate our previous results quantitatively. The implications for skyrmionics as well as topological superconductivity are discussed.

cond-mat.mes-hall↗

arXiv2025

Current-induced Dynamics of Bloch Domain-wall Bimerons

Domain-wall bimerons are composite topological structures formed by embedding bimerons within domain walls in ferromagnets with in-plane anisotropy. These hybrid textures have recently attracted significant attention due to their promise for racetrack memory applications. In this work, we systematically investigate the current-driven dynamics of single domain-wall bimerons and bimeron chains under spin-transfer torque (STT) and spin-orbit torque (SOT). We show that when the spin current is injected or polarized perpendicular to the domain wall, the bimeron Hall effect facilitates efficient motion along the wall. In contrast, spin currents injected or polarized parallel to the wall suppress transverse motion, leading to a significant reduction in the bimeron Hall angle. This anisotropic response is observed for both STT and SOT driving mechanisms. Furthermore, we find that increasing the number of bimerons within a domain wall diminishes their collective mobility. These results provide key insights into domain-wall bimeron dynamics and offer guidance for their integration into bimeron-based spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Antiferromagnetic Chiral Bobber Formation and Topological Proximity Effect in MnBi2Te4

With topological materials being billed as the key to a new generation of nanoelectronics via either functional real-space topological structures (domain walls, skyrmions etc.) or via momentum-space topology (topological insulators), tailored and controllable topological properties are of paramount significance, since they lead to topologically protected states with negligible dissipation, enabling stable and non-volatile information processing. Here, we report on the evolution of topological magnetic textures in the proximity of other topological defects, i.e., antiferromagnetic domain walls in the topological insulator MnBi2Te4. The transition from the antiferromagnetic ground state to a canted antiferromagnetic state at finite magnetic fields is accompanied by the formation of chiral bobbers - bulk-terminated topological defects adjacent to the domain walls in this system, leading to a topological proximity effect.

cond-mat.mes-hall↗

arXiv2025

Unraveling effects of competing interactions and frustration in vdW ferromagnetic Fe3GeTe2 nanoflake devices

Two-dimensional (2D) van der Waals (vdW) magnets and devices have garnered significant attention owing to the stabilization of long range magnetic order down to atomic limit, and the prospect for novel quantum devices with unique functionalities. To achieve this objective, clarification of magnetotransport properties and understanding of the relevant interactions with lowering of dimensions are of extreme importance. Here, the magnetotransport properties of few atomic layer Fe3GeTe2 and (Co0.25Fe0.75)3GeTe2 nanoflake devices have been investigated. Magnetotransport investigations with applied magnetic field along the easy-axis shows anomalous Hall effect, while that for applied magnetic field along the hard-axis reveals an unusual behaviour. Atomistic calculations considering the presence of antiferromagnetic, ferromagnetic and local symmetry-breaking interactions reveal critical role of magnetic frustration effect assisted by thermal fluctuations, leading to a non-zero scalar spin chirality manifesting in an unconventional Hall effect. The present result clarifies the underlying interactions in few-layer 2D vdW ferromagnetic material system, important for the understanding of non-collinear spin configurations in vdW magnets for 2D spintronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Giant Topological Hall Effect in Magnetic Weyl Metal Mn$_{2}$Pd$_{0.5}$Ir$_{0.5}$Sn

The synergy between real and reciprocal space topology is anticipated to yield a diverse array of topological properties in quantum materials. We address this pursuit by achieving topologically safeguarded magnetic order in novel Weyl metallic Heusler alloy, Mn$_{2}$Pd$_{0.5}$Ir$_{0.5}$Sn. The system possesses non-centrosymmetric D$_{2d}$ crystal symmetry with notable spin-orbit coupling effects. Our first principles calculations confirm the topological non-trivial nature of band structure, including 42 pairs of Weyl nodes at/near the Fermi level, offering deeper insights into the observed anomalous Hall effect mediated by intrinsic Berry curvature. A unique canted magnetic ordering facilitates such rich topological features, manifesting through an exceptionally large topological Hall effect at low fields. The latter is sustained even at room temperature and compared with other known topological magnetic materials. Detailed micromagnetic simulations demonstrate the possible existence of an antiskyrmion lattice. Our results underscore the $D_{2d}$ Heusler magnets as a possible platform to explore the intricate interplay of non-trivial topology across real and reciprocal spaces to leverage a plethora of emergent properties for spintronic applications.

cond-mat.mtrl-sci↗

arXiv2023

Chiral Skyrmions Interacting with Chiral Flowers

The chiral nature of active matter plays an important role in the dynamics of active matter interacting with chiral structures. Skyrmions are chiral objects, and their interactions with chiral nanostructures can lead to intriguing phenomena. Here, we explore the random-walk dynamics of a thermally activated chiral skyrmion interacting with a chiral flower-like obstacle in a ferromagnetic layer, which could create topology-dependent outcomes. It is a spontaneous mesoscopic order-from-disorder phenomenon driven by the thermal fluctuations and topological nature of skyrmions that exists only in ferromagnetic and ferrimagnetic systems. The interactions between the skyrmions and chiral flowers at finite temperatures can be utilized to control the skyrmion position and distribution without applying any external driving force or temperature gradient. The phenomenon that thermally activated skyrmions are dynamically coupled to chiral flowers may provide a new way to design topological sorting devices.

cond-mat.mes-hall↗

arXiv2023

Laminar and transiently disordered dynamics of a magnetic skyrmion pipe flow

The world is full of fluids that flow. The fluid nature of flowing skyrmionic quasiparticles is of fundamental physical interest and plays an essential role in the transport of many skyrmions. Here, we report the laminar and transiently disordered dynamic behaviors of many magnetic skyrmions flowing in a pipe channel. The skyrmion flow driven by a uniform current may show a lattice structural transition. The skyrmion flow driven by a non-uniform current shows a dynamically varying lattice structure. A large uniform current could result in the compression of skyrmions toward the channel edge, leading to the transition of the skyrmion pipe flow into an open-channel flow with a free surface. Namely, the width of the skyrmion flow could be adjusted by the driving current. Skyrmions on the free surface may form a single shear layer adjacent to the main skyrmion flow. In addition, although we focus on the skyrmion flow dynamics in a clean pipe channel without any pinning or defect effect, we also show that a variation of magnetic anisotropy in the pipe channel could lead to more complicated skyrmion flow dynamics and pathlines. Our results reveal the fluid nature of skyrmionic quasiparticles that may motivate future research on the complex flow physics of magnetic textures.

cond-mat.mes-hall↗

arXiv2023

Reversible magnetic domain reorientation induced by magnetic field pulses with fixed direction

Nanoscale magnetic domains with controllable configurations could be used for classical and quantum applications, where the switching of magnetization configurations is an essential operation for information processing. Here, we report that the magnetic domain reorientation in a notched ferromagnetic nanotrack can be realized and effectively controlled by applying uniform magnetic field pulses in a fixed in-plane direction perpendicular to the nanotrack. Our micromagnetic simulation results show that the configurations of magnetic domains in the notched nanotrack can be switched between a head-to-head state and a tail-to-tail state in a reversible manner driven by magnetic field pulses, while it is unnecessary to reverse the direction of the magnetic field. Such a unique magnetic domain reorientation dynamics is found to depend on magnetic parameters and nanotrack geometries. The reorientation dynamics of magnetic domains also depends on the strength and length of the applied magnetic field pulse. In addition, we point out that the notches at the center of the nanotrack play an important role for the stabilization of the head-to-head and tail-to-tail states during the magnetic domain reorientation. We also qualitatively explain the field-induced reorientation phenomenon with a simplified two-dimensional macrospin model. Our results may make it possible to build spintronic devices driven by a fixed magnetic field. Our findings may also motivate future studies to investigate the classical and quantum applications based on nanoscale magnetic domains.

cond-mat.mes-hall↗

arXiv2023

Scaling behaviour of the helical and skyrmion phases of Cu2OSeO3 determined by single crystal small angle neutron scattering

Skyrmions are topologically protected quantum objects at the nanometre scale. They form perpendicular to an applied magnetic field at a certain temperature and arrange themselves in a typically hexagonal lattice. Using small angle neutron scattering we have determined the magnetic field versus temperature phase diagrams of the stability range of the different magnetic phases, the helical as well as the skyrmion phases in the multiferroic skyrmion material Cu$_2$OSeO$_3$. Therefore, a single crystal was mounted in different crystal orientations, i.e. unoriented and with the crystallographic $\langle1 1 0\rangle$ and $\langle1 0 0\rangle$ axis aligned parallel to the magnetic field. Furthermore, different cooling procedures were tested, cooling from the paramagnetic phase at zero magnetic field and field cooling through the skyrmion phase where metastable skyrmions are nucleated. From this, not only were the stability ranges of both the helical and skyrmion phases in this multiferroic skyrmion material determined, but the length of the spin helix and the skyrmion distances at different conditions was also determined through detailed analysis of the positions of the observed Bragg peaks. The obtained data provide valuable information about the scaling of the skyrmion distances and therefore their packing density. The knowledge about this tunability will serve as an important input for the theoretical understanding of the formation of skyrmions. Concerning technological applications, for example as high-density data storage devices in information technology, the temperature and magnetic field dependence of the packing density of skyrmions is of critical importance for their design. Therefore, the obtained knowledge is an essential input for future skyrmionics applications in high-density data storage, in low-energy spintronics or in skyrmionics quantum computation.

cond-mat.str-el↗

arXiv2022

Chirality inversion and radius blow-up of a Néel-type skyrmion by a Pearl vortex

We develop a theory for the coaxial configuration of a Néel-type skyrmion and a Pearl vortex in thin superconductor-chiral ferromagnetic heterostructures. Using direct numerical solution of the Euler-Lagrange equation and micromagnetic simulations we demonstrate that the inhomogeneous magnetic field of the Pearl vortex significantly modifies the skyrmion profile with respect to the one in the absence of the vortex. We discover drastic enlargement of the skyrmion's radius and inversion of the skyrmion's chirality. To unravel physics behind these effects we invent novel two-parameter ansatz for the magnetization profile of the skyrmion in the presence of the vortex. Chirality inversion and radius blow-up are controlled not only by the material parameters of the heterostructure but also by the thickness of the superconductor. Our findings can have implications for Majorana modes localized at skyrmion-vortex pairs.

cond-mat.mes-hall↗

arXiv2022

Reversible Transformation between Isolated Skyrmions and Bimerons

Skyrmions and bimerons are versatile topological spin textures that can be used as information bits for both classical and quantum computing. The transformation between isolated skyrmions and bimerons is an essential operation for computing architecture based on multiple different topological bits. Here we report the creation of isolated skyrmions and their subsequent transformation to bimerons by harnessing the electric current-induced Oersted field and temperature-induced perpendicular magnetic anisotropy variation. The transformation between skyrmions and bimerons is reversible, which is controlled by the current amplitude and scanning direction. Both skyrmions and bimerons can be created in the same system through the skyrmion-bimeron transformation and magnetization switching. Deformed skyrmion bubbles and chiral labyrinth domains are found as nontrivial intermediate transition states. Our results may provide a unique way for building advanced information-processing devices using different types of topological spin textures in the same system.

cond-mat.mes-hall↗